Martha Stanbury is with the Michigan Department of Community Health. She says if pools aren't properly maintained, they can make you sick.

It sounds like common-sense advice, but here it is:

"Use the bathroom, not the pool, when you have to pee or poo. Make sure diapers are clean. Don't go swimming if you have diarrhea or your kids have diarrhea, wash off before you get into going swimming," Stanbury says.

She says bacteria in pools can cause gastrointestinal problems. She also says pool owners need to make sure chlorine and P-H levels are carefully monitored.

"You can also get sick from the chemicals associated with pools," Stanbury says. "The chlorine has a chemical reaction with human proteins that are in urine in sweat, and that creates chloramine gas. That's the chlorine you smell when you've been swimming. It can make you have respiratory problems, and people with asthma can get attacks from inhaling chloramines."

In one test of backyard and municipal swimming pools, the Centers for Disease Control found that nearly 60 percent had a "fecal indicator."